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Use of Lightweight Concrete for Reducing Cracks in Bridge Decks
http://www.virginiadot.org/vtrc/main/online_reports/pdf/16-r14.pdf HARIKRISHNAN NAIR, Ph.D., P.E. Research Scientist CELIK OZYILDIRIM, Ph.D., P.E. Principal Research Scientist MICHAEL M. SPRINKEL, P.E. Associate Director
Final Report VTRC 16-R14
Standard Title Page - Report on Federally Funded Project 1. Report No.: 2. Government Accession No.: 3. Recipient’s Catalog No.: FHWA/VTRC 16-R14
4. Title and Subtitle: 5. Report Date: Use of Lightweight Concrete for Reducing Cracks in Bridge Decks April 2016
6. Performing Organization Code:
7. Author(s): Harikrishnan Nair, Ph.D., P.E., Celik Ozyildirim, Ph.D., P.E., and Michael M. Sprinkel, P.E.
8. Performing Organization Report No.: VTRC 16-R14
9. Performing Organization and Address: Virginia Transportation Research Council 530 Edgemont Road Charlottesville, VA 22903
10. Work Unit No. (TRAIS): 11. Contract or Grant No.: 103636
12. Sponsoring Agencies’ Name and Address: 13. Type of Report and Period Covered: Virginia Department of Transportation 1401 E. Broad Street Richmond, VA 23219
Federal Highway Administration 400 North 8th Street, Room 750 Richmond, VA 23219-4825
Final 14. Sponsoring Agency Code:
15. Supplementary Notes: 16. Abstract:
Cracks in bridge decks can be due to many factors related to environmental effects, chemical reactions, and structural loads. Careful selection of materials and mixture proportions can minimize cracking to some degree. To reduce cracking, shrinkage must be reduced; however, cracking also depends on other factors such as modulus of elasticity, creep, tensile strength, and restraint. A low modulus of elasticity and high creep help to minimize cracking.
Lightweight concrete (LWC) has a lower modulus of elasticity, higher inelastic strains, a lower coefficient of thermal
expansion, a more continuous contact zone between the aggregate and the paste, and more water in the pores of aggregates for continued internal curing when compared to normal weight concrete. These properties tend to reduce cracking in the concrete and are highly desirable in bridge decks. The Virginia Department of Transportation (VDOT) has been successfully using LWC in bridge structures. In most of these bridges, the coarse aggregate has been lightweight and the fine aggregate normal weight natural sand.
The purpose of this study was to investigate the effectiveness of LWC in reducing cracks in bridge decks. Seven bridges
from six VDOT districts were included in the study. Three bridge decks each were constructed in 2012 and 2013, and one was constructed in 2014.
The results showed that bridge decks with fewer cracks than were typical of decks constructed with normal weight
aggregate over the past 20 years or no cracks can be constructed with LWC mixtures. The study recommends that LWC with a maximum cementitious content of 650 lb/yd3 be used in VDOT bridge deck concrete mixtures.
17 Key Words: 18. Distribution Statement: lightweight concrete, bridge deck cracking, shrinkage, internal curing, bridge decks
No restrictions. This document is available to the public through NTIS, Springfield, VA 22161.
19. Security Classif. (of this report): 20. Security Classif. (of this page): 21. No. of Pages: 22. Price: Unclassified Unclassified 21
Form DOT F 1700.7 (8-72) Reproduction of completed page authorized
FINAL REPORT
USE OF LIGHTWEIGHT CONCRETE FOR REDUCING CRACKS IN BRIDGE
DECKS
Harikrishnan Nair, Ph.D., P.E.
Research Scientist
Celik Ozyildirim, Ph.D., P.E.
Principal Research Scientist
Michael M. Sprinkel, P.E.
Associate Director
In Cooperation with the U.S. Department of Transportation
Federal Highway Administration
Virginia Transportation Research Council
(A partnership of the Virginia Department of Transportation
and the University of Virginia since 1948)
Charlottesville, Virginia
April 2016
VTRC 16-R14
ii
DISCLAIMER
The contents of this report reflect the views of the authors, who are responsible for the
facts and the accuracy of the data presented herein. The contents do not necessarily reflect the
official views or policies of the Virginia Department of Transportation, the Commonwealth
Transportation Board, or the Federal Highway Administration. This report does not constitute a
standard, specification, or regulation. Any inclusion of manufacturer names, trade names, or
trademarks is for identification purposes only and is not to be considered an endorsement.
Copyright 2016 by the Commonwealth of Virginia.
All rights reserved.
iii
ABSTRACT
Cracks in bridge decks can be due to many factors related to environmental effects,
chemical reactions, and structural loads. Careful selection of materials and mixture proportions
can minimize cracking to some degree. To reduce cracking, shrinkage must be reduced;
however, cracking also depends on other factors such as modulus of elasticity, creep, tensile
strength, and restraint. A low modulus of elasticity and high creep help to minimize cracking.
Lightweight concrete (LWC) has a lower modulus of elasticity, higher inelastic strains, a
lower coefficient of thermal expansion, a more continuous contact zone between the aggregate
and the paste, and more water in the pores of aggregates for continued internal curing when
compared to normal weight concrete. These properties tend to reduce cracking in the concrete
and are highly desirable in bridge decks. The Virginia Department of Transportation (VDOT)
has been successfully using LWC in bridge structures. In most of these bridges, the coarse
aggregate has been lightweight and the fine aggregate normal weight natural sand.
The purpose of this study was to investigate the effectiveness of LWC in reducing cracks
in bridge decks. Seven bridges from six VDOT districts were included in the study. Three
bridge decks each were constructed in 2012 and 2013, and one was constructed in 2014.
The results showed that bridge decks with fewer cracks than were typical of decks
constructed with normal weight aggregate over the past 20 years or no cracks can be constructed
with LWC mixtures. The study recommends that LWC with a maximum cementitious content of
650 lb/yd3 be used in VDOT bridge deck concrete mixtures.
1
FINAL REPORT
USE OF LIGHTWEIGHT CONCRETE FOR REDUCING CRACKS IN BRIDGE
DECKS
Harikrishnan Nair, Ph.D., P.E.
Research Scientist
Celik Ozyildirim, Ph.D., P.E.
Principal Research Scientist
Michael M. Sprinkel, P.E.
Associate Director
INTRODUCTION
Bridge deck cracking is a major and costly problem as it often accelerates corrosion,
increases maintenance costs, and shortens the service life of the deck. Cracks in bridge decks
can be due to many factors related to environmental effects, chemical reactions, plastic
shrinkage, drying shrinkage, and structural loads. Low permeability and a proper air void system
do not always ensure durability if the concrete contains excessive cracks that facilitate the
intrusion of aggressive solutions.
Effective control of early-age cracking can result in limited later-age cracking and can
reduce chloride penetration and corrosion potential (Darwin and Browning, 2008). Careful
selection of materials and mixture proportions can minimize cracking to some degree. Mixtures
with high water and paste contents are prone to shrinkage cracks that occur over a period of time.
Use of large-size aggregate and well-graded aggregates reduces the water and paste contents and
minimizes shrinkage (Ozyildirim, 2007). To reduce cracking, shrinkage must be reduced;
however, cracking also depends on other factors such as modulus of elasticity, creep, tensile
strength, and restraint. A low modulus of elasticity and high creep help minimize cracking.
Lightweight concrete (LWC) has a lower modulus of elasticity, higher inelastic strains, a
lower coefficient of thermal expansion, a more continuous contact zone between the aggregate
and the paste, and more water in the pores of aggregates for continued internal curing when
compared to normal weight concrete (NWC). These properties tend to reduce cracking in the
concrete and are highly desirable in bridge decks. Weiss et al. (1999) established that a reduced
modulus of elasticity can reduce the potential cracking of the concrete. Having a lower modulus
of elasticity, a concrete can be considered more flexible than one with a greater modulus.
Therefore, less rigidity of the concrete can provide better performance, reducing early-age
cracking that is caused by thermal displacement, autogenous shrinkage, moisture loss, and
restrained shrinkage. Further, NWC weighs about 150 lb/ft3 as compared to structural LWC that
weighs about 115 to 120 lb/ft3. This is significant since using LWC decreases the dead load of
NWC by about 20% (Ozyildirim and Gomez, 2005).
2
The Virginia Department of Transportation (VDOT) has been successfully using LWC in
bridge structures. In most of these bridges, the coarse aggregate has been lightweight and fine
aggregate normal weight natural sand. In general, the resistance to cycles of freezing and
thawing and the wear resistance of these concretes have been satisfactory (Ozyildirim, 2008). In
1979, VDOT constructed a bridge deck with LWC that had coarse aggregate with a very high
absorption of 18%. This 212-ft-long bridge is located on old Route 60 (now Route 269) over the
Cowpasture River. It has two lanes and two spans with a continuous deck on steel beams.
Cylinders tested during construction had an average 28-day compressive strength of 5,100 psi
(Ozyildirim, 2008). In 2013 a visual survey indicated the deck was still in very good condition
after 34 years of service. It had no transverse cracks (common on continuous bridges), no visible
cracks, and very limited wear. It had some shallow pop outs exposing the coarse aggregate in
some areas, as shown in Figure 1. Another bridge on Route 60 over the Maury River also had an
LWC deck, and no cracks were found in as 2013 survey after 30 years of service.
Early-age cracking of concrete bridge decks can have several detrimental effects on long-
term behavior and durability. It is imperative that bridge deck concrete be proportioned and
placed so as to minimize early-age cracking.
Full-depth transverse cracking is typically observed in VDOT’s newly constructed bridge
decks. Figures 2 and 3 shows transverse cracks found on Nimmo Parkway (Hampton Roads
District) and Route 61 over the New River in VDOT’s Salem District constructed in 2014 using
standard VDOT Class A4 NWC.
Figure 1. Lightweight Concrete Bridge Deck at Route 269 After 34 Years
3
Figure 2. Transverse Cracks on Nimmo Parkway (Hampton Roads District)
Figure 3. Transverse Cracks on Route 61 Over New River (Salem District)
Transverse bridge deck cracking with a crack density of 0.186 ft/ft2
was also observed on
the U.S. 15 bridge crossing the James River soon after its construction in 2000 (Saloman and
Moen, 2015). Sharp and Moruza (2009) documented transverse cracks with a crack density of
0.0624 ft/ft2
on two bridges on U.S. 123 over the Occoquan River that were completed in 2007.
Both bridge decks were placed with standard VDOT Class A4 NWC.
4
PURPOSE AND SCOPE
The purpose of this study was to investigate the effectiveness of LWC in reducing cracks
in bridge decks. Seven bridges from six VDOT districts were included in the study. Three
bridge decks each were constructed in 2012 and 2013, and one was constructed in 2014.
METHODS
Four tasks were conducted to fulfill the purpose of the study.
1. Several VDOT bridges were selected for using LWC mixtures.
2. Bridge deck placement details were documented with emphasis on the concrete and
air temperatures at the time of placement and during the first 24 hours of the concrete
curing period.
3. Concrete mixtures were collected to determine fresh concrete properties, and field
samples were prepared and tested for hardened concrete properties. Testing in
accordance with ASTM C157 provides an accepted indication of shrinkage.
4. Field evaluations of the bridge decks were conducted through crack surveys at
varying intervals to allow comparison of the frequency and width of cracks in the
decks constructed with lightweight aggregate to typical values of decks constructed in
the last 20 years with normal weight aggregate. Both drying shrinkage and thermal
contraction can contribute to the incidence of cracking.
Bridge Details
The seven study bridges were located in VDOT’s Northern Virginia, Staunton,
Lynchburg, Culpeper, Richmond, and Fredericksburg districts. Details of the bridges including
length, width, type of beam and skew angle (if any), and construction year are shown in Table 1.
Mix Design
The decks were constructed with mixtures containing different cementitious contents
(635 to 705 lb/yd3), fine aggregates, and mineral admixtures. Expanded slate lightweight coarse
aggregate was used in all mixtures. Commercially available air-entraining, water-reducing, and
retarding admixtures were also used. The LWC mixture proportions (per cubic yard) used for
the bridge decks are shown in Table 2.
5
Table 1. Details of Study Bridges That Used Lightweight Concrete in the Deck
Route No./District
Length (ft)
Width (ft)
No. of Spans
Type of Beam Support
Skew Angle
(Degrees)
Construction Year 2012
Route 657, Senseny Road, Winchester/ Staunton 249 32 4 Steel 0
Route 128, Chandlers Mountain Road, Lynchburg/Lynchburg 264 36 4 Steel 0
Route 15, Opal/Culpeper 256 28 2 Lightweight concrete beams 27
Construction Year 2013
Route 49, The Falls Road, Crewe/
Richmond
175 42 3 Steel 0
Route 646, Aden Road, Nokesville/Northern Virginia 167 32 3 Prestressed concrete slab 0
Route 3, Piankatank River, Mathews County/Fredericksburg 4186 28 30 Steel 0
Construction Year 2014
I-95 HOV Lane, Stafford/Northern Virginia 159 48 1 Steel 0
Table 2. Lightweight Concrete Mix Designs (Lightweight Mixture Proportions per Cubic Yard)
Ingredient
Route 657
Winchester
Route 128
Lynchburg
Route 15
Opal
Route 49
Crewe
Route 646
Nokesville
Route 3
Matthews
County
I-95 HOV Lane
Stafford
705 lb
cementitious
25% fly ash
635 lb
cementitious
50% slag
660 lb
cementitious
50% slag
696 lb
cementitious
24.5% fly ash
675 lb
cementitious
20% fly ash
635 lb
cementitious
20% fly ash
660 lb
cementitious
50% slag
8/14/12 9/26/12 10/24/12 10/22/13 8/21/13 11/8/13 2/20/14
Cement (lb) 529 318 330 525 540 508 330
Fly ash (lb) 176 - - 171 135 127 -
Slag (lb) - 317 330 - - - 330
Fine aggregate (sand)
(lb)
1358 1268 1285 1161 1295 1365 1305
Coarse aggregate
(Stalite) (lb)
824 900 893 891 837 850 850
Water (lb) 267 286 292 313 292 286 292
w/cm 0.38 0.45 0.44 0.45 0.43 0.45 0.44
w/cm = water–cementitious material ratio.
6
Field Placement Documentation and Fresh Concrete Properties
Bridge deck construction details were documented including the concrete placement
method (pumping, etc.). Concrete temperature, air temperature, relative humidity, and wind
speed were also monitored throughout the study. The concrete properties were determined in the
fresh and hardened states. In the fresh state, the concretes were tested for slump (ASTM C143),
air content (ASTM C173), and density (unit weight, ASTM C138).
Hardened Concrete Properties
Concrete mixtures were collected from different truckloads, and specimens were
prepared for hardened concrete testing. Table 3 provides a list of the hardened concrete
properties tested and their respective specifications. Three specimens each were used for testing
compressive strength, elastic modulus, splitting tensile strength, and drying shrinkage. Two
samples each were used for freeze-thaw and permeability testing. Drying shrinkage test
specimens were subjected to 7 days of moist curing. Permeability (reported as coulomb values)
specimens were subjected to an accelerated moist cure for 1 week at room temperature and then
3 weeks at 100 °F. The resistance to cycles of freezing and thawing was determined in
accordance with ASTM C666, Procedure A, except that the specimens were air dried at least 1
week before the test and the test water contained 2% NaCl. The acceptance criteria at 300 cycles
are a weight loss of 7% or less, a durability factor of 60 or more, and a surface rating of 3 or less.
Table 3. Hardened Concrete Tests and Specimen Sizes
Test Specification Size (in)
Compressive strength ASTM C39 4 x 8
Elastic modulus ASTM C469 4 x 8
Splitting tensile strength ASTM C496 4 x 8
Permeability VTM 112 2 x 4
Drying shrinkage ASTM C157 3 x 3 x 11
Freeze-thaw durability ASTM C666 3 x 4 x 16
Crack Surveys
Crack surveys of the bridge decks were conducted at different intervals. The crack survey
procedure included measuring the crack lengths and widths. Crack density was also calculated (as
the sum of all crack lengths divided by the area of the deck).
RESULTS AND DISCUSSION
Field Placement Documentation and Fresh Concrete Properties
The bridge decks for Route 657 Winchester, Route 128 Lynchburg, and Route 15 Opal
were constructed in 2012. The fresh concrete properties are shown in Table 4. LWC mixture
was placed by pumping for all three bridges. For all three bridges, the fresh concrete properties
7
met VDOT specifications. Average slumps ranged from 4 to 8 in, and air content ranged from
5.5% to 8%. For Route 657 Winchester, the LWC mixture contained a total cementitious content
of 705 lb/yd3, of which 25% was fly ash. Route 128 Lynchburg and Route 15 Opal used LWC
mixtures with cementitious contents of 635 and 650 lb/yd3, respectively, of which 50% was slag.
The water–cementitious materials ratio (w/cm) was 0.38, 0.45, and 0.44, respectively, for Route
657 Winchester, Route 128 Lynchburg, and Route 15 Opal. To reduce the amount of water loss
during construction and to avoid plastic shrinkage, VDOT requires that the evaporation rate
during construction be below 0.1 lb/ft2/hr. The concrete evaporation rates were very low (less
than 0.1 lb/ft2/hr) in all three cases. All decks were wet cured for 7 days. After completion of
the wet curing, a curing compound was applied to the surface of the decks. Then, the decks were
grooved.
Table 4. Fresh Concrete Properties for Route 657 Winchester, Route 128 Lynchburg, and Route 15 Opal
Fresh Property
Route 657 Winchester Route 128 Lynchburg Route 15 Opal
8/14/12 9/26/12 10/24/12
Batch 1 Batch 2 Batch 1 Batch 2 Batch 1 Batch 2
Unit Weight, lb/ft3 120.9 117.2 115.6 114.2 - -
% Air 6.2 8.0 7.1 6.8 5.5 7.6
Slump, in 5.0 8.0 5.5 6.75 4.0 5.0
Temperature (oF)
Concrete 86 79 69 68 69 68
Air 73 79 58 58 61 -
% Relative Humidity 73 69 86 79 84 -
Wind, mph 0.0 0 1.5 3.0 0.6 -
Evaporation rate, lb/ft2/hr 0.021 0.025 0.03 0.04 0.0 -
The bridge decks for Route 646 Nokesville, Route 49 Crewe, and Route 3 Matthews
County were constructed in 2013. The fresh concrete properties are shown in Table 5. Route
646 Nokesville, Route 49 Crewe, and Route 3 Mathews County used total cementitious contents
of 675, 696, and 635 lb/yd3, respectively, with 20%, 25%, and 20% fly ash, respectively.
Corresponding w/cms were 0.43, 0.45, and 0.45, respectively. For Route 646 Nokesville and
Route 3 Mathews County, the LWC mixtures were placed directly from the truck mixer. For
Route 49 Crewe, the LWC mixture was placed by pumping. The concrete slump, air content,
and evaporation rate met VDOT specifications. All three bridges decks were placed in multiple
pours.
Each lane of Route 646 Nokesville was cast in 2 days. The eastbound lane, Spans 2 and
3, excluding the closure pour, were constructed on 8/21/13, and Span 1 and both closure pours
were placed on 8/27/13. All three spans of the westbound lane excluding the two closure pours
were placed on 10/19/13, and the closure pours were placed on 10/22/13. The closure pours
were 4 ft wide, centered on the piers.
The bridge deck for I-95 HOV Lane Stafford was constructed in 2014. Table 6 shows the
fresh concrete properties. The LWC mixture was placed by a conveyer system. The
cementitious content of the mixture was 660 lb/yd3, of which 50% was slag. A w/cm of 0.44
was used.
8
Table 5. Fresh Concrete Properties of Route 646 Nokesville, Route 49 Crewe, and Route 3 Mathews County
Fresh Property
Route 646 Nokesville
Lightweight Deck
Route 49 Crewe
Lightweight Pour
Route 3 Mathews County
8/21/13 10/22/13 11/8/13
Batch 1 Batch 2 Batch 1 Batch 2 Batch 1 Batch 2
Unit Weight, lb/ft3 114.0 122.0 115.6 115.2 114.7 114.7
% Air 5.5 5.2 5.2 5.2 6.3 8
Slump, in 5.0 5.0 6.25 6.5 6.0 6.5
Temperature (oF)
Concrete 80 84 71 73 66 70
Air 70 68 28.9 28.8 52 45
% Relative Humidity 90 93 82 74 53 40
Wind, mph 0.0 1.2 0.6 0 6.7 7.3
Evaporation rate, lb/ft2/hr 0.02 0.04 0.03 0.03 0.09 0.13
Table 6. Fresh Concrete Properties for I-95 HOV Lane Stafford
Fresh Property
2/20/14
Batch 1 Batch 2
Unit Weight, lb/ft3 117.6 118.4
% Air 6.5 6
Slump, in 6.0 5.0
Temperature (oF)
Concrete 64 64
Air 53 54
% Relative Humidity 23 23
Wind, mph 3.1 5.9
Evaporation rate, lb/ft2/hr 0.06 0.09
Hardened Concrete Properties of Field Samples
The hardened concrete properties for all three bridge decks constructed in 2012 are
shown in Table 7. The average 28-day strength for Route 657 Winchester ranged from 5,320 psi
to 5,450 psi. The average 28-day strength for two batches for Route 128 Lynchburg and Route
15 Opal were 5,480 psi and 5,920 psi, respectively. Even though the Route 657 Winchester
LWC mixture had a higher cementitious content and a lower w/cm compared to the other two
bridges, strength results were comparable, which indicates that a w/cm higher than 0.38 was used
for Route 657 Winchester. The average elastic modulus ranged from 3.09 * 106 psi to 3.43 * 10
6
psi. Permeability values ranged from 395 C to 1174 C. All specimens showed excellent
resistance to cycles of freezing and thawing.
The drying shrinkage values for all three bridge mixtures are shown in Figure 4. The
drying shrinkage values after a 28-day drying period for all specimens were below 0.03% except
for Route 657 Winchester (values were approximately 0.05%). It can be seen that as
cementitious content increases, drying shrinkage values also increase. Lower cement, water, and
paste contents are always desirable to lower cracking including those related to drying shrinkage.
The hardened concrete properties for Route 128 Lynchburg confirm that decks can be
successfully placed using LWC with a cementitious content below 650 lb/yd3 while meeting
strength and permeability requirements. The industry also accepts that LWCs with a maximum
cementitious material content of 650 lb/yd3 can be prepared and placed successfully.
9
Table 7. Hardened Concrete Properties for Route 657 Winchester, Route 128 Lynchburg, and Route 15 Opal
Hardened Property
Route 657 Winchester Route 128 Lynchburg Route 15 Opal
8/14/12 9/26/12 10/24/12
Batch 1 Batch 2 Batch 1 Batch 2 Batch 1 Batch 2
Compressive Strength, psi
3-day 3640 3600 2060 1870 2730 2630
7-day 4130 4000 3470 3370 4040 3620
28-day 5320 5450 5470 5490 5940 5890
Elastic Modulus (106 psi)
7-day 2.96 2.95 2.82 2.82 2.84 2.82
28-day 3.09 3.17 3.43 3.29 3.22 3.29
Splitting Tensile Strength, psi 425 490 515 470 435 475
Permeability, coulomb, C 914 874 395 419 1174 766
Freeze-Thaw Durability
% Weight loss 1.59 5.25 4.1 4.8 6.6 7.5
Durability factor 106 101 101 104 114 116
Surface rating 0.53 1.28 1.0 1.0 1.5 1.6
10
Figure 4. Drying Shrinkage Results for Route 657 Winchester, Route 128 Lynchburg, and Route 15 Opal
The hardened concrete properties of all three bridges constructed in 2013 are shown in
Table 8. For Route 646 Nokesville, the average 28-day strength results for Batch 1 and Batch 2
showed large variation. As mentioned before, the deck for Route 646 Nokesville was placed on
different days. For the eastbound lane, two batches of concrete were tested by the Virginia
Transportation Research Council (VTRC), and the results are summarized in Table 8. Since this lane
exhibited extensive cracking, more data were collected by the field personnel: 28-day strengths of
8,580 psi, 7,630 psi, and 6,990 psi were obtained. For LWC, it is very important to pre-soak the
lightweight aggregate before mixing. The reason for the different average strength results was the
lack of proper saturation of the lightweight aggregates.
For Route 49 Crewe and Route 3 Mathews County, the average 28-day strengths were 5,760
psi and 5,770 psi, respectively. All specimens showed excellent resistance to freezing-thawing.
Permeability values ranged from 473 C to 964 C.
-0.1
-0.09
-0.08
-0.07
-0.06
-0.05
-0.04
-0.03
-0.02
-0.01
0
0.01
1 7 10 14 21 35 63 119 231 455
Len
gth
Chan
ge
(%)
Time (days)
Winchester- Batch 1
Winchester-Batch 2
Lynchburg-Batch1
Lynchburg-Batch 2
Opal-Batch 1
Opal-Batch 2
635 lb/yd^3
660 lb/yd^3
705 lb/yd^3
11
Table 8. Hardened Concrete Properties for Route 646 Nokesville, Route 49 Crewe, and Route 3 Mathews County
Hardened Property
Route 49 Crewe
Lightweight Pour
Route 646 Nokesville
Lightweight Deck
Route 3
Mathews County
10/22/13 8/21/13 11/8/13
Batch 1 Batch 2 Batch 1 Batch 2 Batch 1 Batch 2
Compressive Strength, psi
3-day 3720 3840 2870 5500 3910 3810
7-day 4200 4510 3770 6590 4710 4520
28-day 5490 6020 4870 8010 5840 5690
Elastic Modulus (106 psi)
7-day 3.30 3.00 2.77 3.12 3.26 3.37
28-day 3.08 3.35 3.09 3.82 3.65 3.51
Splitting Tensile Strength, psi 510 550 450 475 540 570
Permeability, coulomb, C 522 473 732 638 912 964
Freeze-Thaw Durability
% Weight loss 0.9 0.3 0.4 0.4 0.4 0.5
Durability factor 112 111 98 96 98 98
Surface rating 0.4 0.4 0.6 0.4 0.6 0.6
12
The drying shrinkage results for all three bridge mixtures are shown in Figure 5. The
drying shrinkage values after the 28-day drying period for all specimens were close to 0.04%.
The bridge deck for I-95 HOV Lane Stafford was placed on 2/20/14 with a single placement.
The average 28-day compressive strength and permeability were 4,620 psi and 497 C, respectively
(Table 9). The drying shrinkage results are shown in Figure 6. The 28-day drying shrinkage was
higher (0.05%) compared to other mixtures in this study.
Figure 5. Drying Shrinkage Results for Route 646 Nokesville, Route 49 Crewe, and Route 3 Mathews County
Table 9. Hardened Concrete Properties for I-95 HOV Lane Stafford
Hardened Property
2/20/14
Batch 1 Batch 2
Compressive Strength, psi
3-day 1120 1250
7-day 1850 2290
28-day 4380 4850
Elastic Modulus 28-day
(106 psi)
2.78 2.83
Splitting Tensile Strength,
psi
465 510
Permeability, coulomb, C 522 473
Freeze-Thaw Durability
Weight loss (%) 6.2 5.2
Durability factor 109 108
Surface rating 0.6 1.1
-0.0800
-0.0700
-0.0600
-0.0500
-0.0400
-0.0300
-0.0200
-0.0100
0.0000
0.0100
0 7 10 14 21 35 63 119 231 455
Len
gth
Ch
an
ge
(%.)
Time (days)
Rte.49 Batch 1Rte.49 Batch 2Rte.646 Batch 1Rte.646 Batch 2Rte.3 Batch 1Rte.3 Batch 2
13
Figure 6. Drying Shrinkage Results for I-95 HOV Lane Stafford
Crack Surveys
Construction Year 2012
Route 657 Winchester
The condition surveys were conducted on 1/31/13 and 2/4/14. There were no cracks on
the deck during either survey.
Route 128 Lynchburg
The condition surveys were conducted on 3/13/13 and 2/21/14 at ages of 6 months and 17
months, respectively. There were no transverse cracks on the deck. Very small longitudinal
cracks (2 to 3 in long with a width less than 0.08 mm) were found in the deck during the survey.
These cracks will have little if any impact on the performance of the decks.
Route 15 Opal
During inspection after the first winter on 9/27/13, no cracks were visible on the deck.
Although the bridge deck showed no cracking, the inspection on September 27 indicated that
cracking had appeared on both the east and west bridge deck approach slabs, which had NWC.
In the right-hand lane of the west approach slab, cracks appeared approximately 45 degrees from
the centerline. One crack originated at the start of the approach slab and ran for 17 ft at a width
of 0.30 mm before expanding to a width of 0.35 mm for another 3 ft. Another crack originated
12 ft from the start of the approach slab and ran for 8 ft at a width of 0.30 mm. On the east
approach slab, there was one crack in the left-hand lane, originating approximately 13 ft from the
start of the slab and running for 7.5 ft at a width of 0.25 mm. This crack ran about 45 degrees to
the centerline. The bridge was opened to traffic on 11/11/13.
-0.09
-0.08
-0.07
-0.06
-0.05
-0.04
-0.03
-0.02
-0.01
0
0.01
0.02
1 7 10 14 21 35 63 119 231 455
Len
gth
Ch
an
ge
(in
)
Time (days)
Batch 1
Batch 2
14
Another condition survey was conducted on 2/24/14. There were no cracks on the LWC
deck; however, the cracks at the NWC approach slab were a similar length but a little wider than
before; about 0.4 mm to 0.5 mm at the east end and 0.5 mm to 0.6 mm at the west end. The
increase in width from the previous September survey was attributed mainly to the cooler
temperature. One other observation was the apparent scaling at a portion of the closure pour that
had LWC, as shown in Figure 7. Since it was restricted to a small area, it was attributed to poor
finishing practices. The rest of the deck including the closure pour was in good condition.
Figure 7. Scaling at Closure Pour of Route 15 Opal Bridge at Lower Middle Portion of Photograph
Construction Year 2013
Route 49 Crewe
The initial condition survey was conducted on 5/20/14 at an age of 7 months. There were
no cracks on the deck.
Route 646 Nokesville
As mentioned before, Route 646 Nokesville was constructed in two stages using four
placements. The eastbound lane comprised Placements 1 and 2. The condition survey of Route 646
Nokesville was conducted on 6/5/14 at an age of 10 months. The crack survey (Figure 8) showed
that the eastbound lane had serious cracking issues, including the closure pour. On the eastbound
lane, Placement 1 (Spans 2 and 3) had crack density of 0.15 ft/ft2 and Placement 2 (Span 3 and two
closure pours) had a crack density of 0.13 ft/ft2. In Spans 1 and 3, there were very large transverse
cracks. Several longitudinal cracks were also found in the eastbound lane. The westbound lane was
placed on a different day, and there were no cracks in the deck, including the closure pour. The
cracks in the eastbound lane may be attributed to a lack of pre-saturation of lightweight aggregate
prior to mixing, which resulted in inconsistent quality concrete with varying strengths.
15
Figure 8. Crack Survey Plots for Route 646 Nokesville (not to scale)
Span 3
Patch
Eastbound
Closure Pour
Pour
Span 2 Span 1
Westbound
16
Route 3 Mathews County
The initial condition survey of Route 3 Mathews County was conducted at an age of 22
months. The bridge was in good condition with no transverse cracks. However, there were a few
cracks on the closure pour, which had also LWC.
Construction Year 2014
I-95 HOV Lane Stafford
The condition surveys of I-95 HOV Lane Stafford were conducted on 5/27/14 and
11/19/14 at ages of 3 months and 9 months, respectively. There were no cracks on the deck.
However, several cracks were found in the approach slab, which had NWC.
CONCLUSIONS
Bridge decks with reduced or no cracks can be constructed with LWC mixtures.
Properly air-entrained LWC made with high-quality lightweight aggregate provides
satisfactory resistance to cycles of freezing and thawing.
Pre-soaking of lightweight aggregate is very important in obtaining consistent quality LWC
and reducing cracking.
Low-permeability LWC can be produced with supplementary cementitious material.
Reduced cracks or no cracks on the deck indicate the benefits of LWC.
VDOT uses 0.035% at 28 days as the maximum shrinkage for the NWC used in bridge decks.
However, the LWCs used in this study had values as high as 0.060% and did not crack. This
shows the benefits of the lower elastic modulus, internal curing, and the lower coefficient of
thermal expansion of LWC.
Decks can be successfully placed using LWC with a cementitious content below 650 lb/yd3
while meeting strength and permeability requirements. Lower cement, water, and paste
contents are always desirable to lower cracking, including those related to drying shrinkage.
The industry accepts that LWCs with a maximum cementitious material content of 650 lb/yd3
can be prepared and placed successfully.
17
RECOMMENDATIONS
1. VDOT’s Materials Division and Structure and Bridge Division should continue to use LWC
in bridge deck concrete mixtures. Further, VDOT’s Structure and Bridge Division should
encourage the use of LWC in bridge decks by incorporating this recommendation into the
Manual of the Structure and Bridge Division.
2. VDOT’s Materials Division and Structure and Bridge Division should specify a maximum
cementitious content of 650 lb/yd3 and maximum fresh unit weight of 120 lb/ft
3 for LWC
bridge deck mixtures.
BENEFITS AND IMPLEMENTATION
Benefits
In 2002, a study estimated that the annual direct costs associated with corrosion of
highway bridges totaled $8.3 billion. The indirect costs to the users were 10 times that value
(Yunovich et al., 2002). Cracking in bridge structures is mainly attributable to moisture loss and
temperature change. LWCs are expected to eliminate deck cracking or at least reduce the
number and width of cracks, which is important for extending the service life of decks.
LWC is expected to be durable in bridge decks because of the reduced cracking attributed
to the modulus compatibility between the paste and the lightweight aggregates, reduced elastic
modulus, and internal curing. Another advantage of using LWC is the reduced weight, which
allows widening of bridges without the need to reinforce or add substructure elements such as
piles, which reduces both the cost and the environmental impact. The increased durability of
LWC leads to a longer lasting material that will reduce future maintenance and repair costs.
Implementation
In Recommendation 1, the study recommended that VDOT’s Materials Division and
Structure and Bridge Division continue to use LWC in bridge deck concrete mixtures and that
the Structure and Bridge Division should encourage the use of LWC in bridge decks by
incorporating this recommendation into the Manual of the Structure and Bridge Division
In Recommendation 2, the study recommended that VDOT’s Materials Division and
Structure and Bridge Division specify a maximum cementitious content of 650 lb/yd3 and a
maximum fresh unit weight of 120 lb/ft3 for LWC bridge deck mixtures. This recommendation
has been accepted and implemented. The recommendation was incorporated into the 2016
VDOT Road and Bridge Specifications. Several ongoing projects are currently using LWC in
bridge decks.
18
ACKNOWLEDGMENTS
The authors thank Michael Burton, Lew Lloyd, and Andy Mills of VTRC for their
outstanding efforts in sample collection and testing. In addition, the assistance of Sam
Heiberger, undergraduate research assistant, in compiling and analyzing data is acknowledged.
Appreciation is also extended to Linda Evans of VTRC for her editorial assistance. The authors
thank staff of VDOT’s Materials Division and Structure and Bridge Division and district
materials and bridge engineers. The authors are also appreciative of the technical review panel
for their expertise and guidance: Larry Lundy, Adam Matteo, and Chaz Weaver of VDOT and
Shabbir Hossain of VTRC.
REFERENCES
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Ozyildirim, C. Durability of Structural Lightweight Concrete. ESCSI Special Workshop on
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Ozyildirim, C., and Gomez, J.P. First Bridge Structure With Lightweight High-Performance
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